Micro-capsules for the sustained release of drugs

ABSTRACT

Micro-capsules for the slow release of drugs, consisting of a lactic-co-glycolic copolymer to which a plasticizer has been incorporated and which contain a drug of pharmaceutical interested within them.

[0001] The present invention relates to a new type of micro-capsule ormicro-bead for the sustained administration of drugs and to a procedurefor their preparation.

[0002] A large variety of administration systems have been proposed fordrugs that require administration over a long time period. The strategydescribed in the literature as the most successful is that ofmicro-encapsulation of the drug to administer in a polymer material ofthe biodegradable and biocompatible polyester type, such aspolylactic-co-glycolic (PLGA). There are a large number of bibliographicreferences to this strategy, such as: U.S. Pat. No. 5,445,832; ES2009346; CH 661 206; CH 665 558; ES 2037621; U.S. Pat. No. 4,652,441; ES2020890; U.S. Pat. Nos. 4,728,721; 5,330,767; 4,917,893; 4,652,441; EP 0145 240; EP 0 2020 065; EP 0 190 833, among others for example.

[0003] These polymers have the peculiarity that they are degraded slowlywithin the body releasing the drug contained inside, and the products ofthis degradation (lactic acid and glycolic acid) are naturally presentwithin the organism.

[0004] In the micro-capsules described in the literature of the state ofthe art it is very hard to achieve a satisfactory modulation of theencapsulated drug release, and to avoid an initial large drug release,as this can only be achieved by changing the composition of the polymer(the ratio of lactic-glycolic acid or the molecular weight thereof),which usually implies making important changes in the procedure for theproduction of the micro-capsules every time a modification in the drugrelease profile is desired.

[0005] In the article published by Pitt el al. in the Journal ofBiomedical Materials Research, Vol. 13, pg 497-507, 1979, it isdescribed that tributyl citrate accelerates the release of drugs, forexample, progesterone, in microcapsules of polylactic polymers.

[0006] As a fruit of our research, we have surprisingly discovered thatthe addition of small amounts of citric acid esters, to the polymerconstituting the micro-capsules, allows a very effective modulation ofthe liberation characteristics of the micro-capsules obtained, withoutthe need to modify the composition of the polymer.

[0007] In the present specification the term modulating release frommicrocapsules is understood to mean a reduction in the initial releaseof encapsulated drug and a release of said drug that is almost linear intime. It is both surprising and unexpected, in view of that described byPitt et al. that the incorporation of small amounts of citric acid esterinto the microcapsule preparation of lactic-co-glycolic polymer thatencapsulate a peptide of pharmaceutical interest allows the release ofthe drug to be almost linear and without the presence of sudden initialreleases of the drug.

[0008] Therefore, the object of this invention consists of providingpharmaceutical of prepartions micro-capsules of polymers of lactic andglycolic acid plastified with small quantities of citric acid esters andwhich contain peptides.

[0009] The present invention also comprises the preparation and use ofthe aforementioned microcapsules.

[0010] The citric acid esters useful for the purposes of the presentinvention are those normally used as plasticizers for pharmaceuticalpolymers, such as triethyl citrate, tributyl citrate and acetyl tributylcitrate. Use of triethyl citrate is preferable.

[0011] By peptides of pharmaceutical interest it is understood:

[0012] analogues of LHRH such as tryptoreline, leuprolide, gosereline,busereline or cetrorelix

[0013] analogues of somatostatin such as somatostatin or octreotide

[0014] analogues of human calcitonin such as salmon calcitonin orcarbocalcitonin.

[0015] The preparation of the micro-capsules can be carried outfollowing any of the methods described in the literature such as, forexample, those described in the U.S. Pat. No. 3,773,919. By way ofdescription and without limitation thereto, the different procedures forproducing micro-capsules of the invention would be grouped into thefollowing sections:

[0016] a) Method of Coacervation:

[0017] A solution of polymer is prepared along with tri-ethyl citrate ina suitable solvent. The drug to be encapsulated is suspended in thepolymer and plasticiser solution and a non-solvent of the polymer isadded to force deposition of the polymer on the drug crystals. Examplesof these procedures without using plasticiser can also be found indocuments such as ES 2009346 or EP 052 510.

[0018] b) Double Emulsion Methods:

[0019] The drug to be encapsulated is dissolved in water or in asolution of some other co-adjuvant in is emulsified in a solution of thepolymer and the plasticiser in a suitable solvent such asdichloromethane for example. The resulting emulsion is in turnemulsified in water or in an aqueous solution of an emulsifier such aspolyvinylic alcohol. Once this second emulsion has been carried out thesolvent in which the polymer was dissolved is eliminated throughevaporation or extraction. The resulting micro-capsules are obtaineddirectly by filtration. Examples of these procedures that do not use theplasticiser can also be found in documents such as U.S. Pat. No.4,652,441.

[0020] c) Simple Emulsion Method:

[0021] The drug to be encapsulated, the polymer and the plasticiser aredissolved together in a suitable solvent. This solution is emulsified inwater or a solution of an emulsifier such as polyvinyl acid and theorganic solvent eliminated by evaporation or extraction. The resultingmicro-capsules are recovered by filtration. Examples of these proceduresthat do not sue the plasticiser can also be found in documents such asU.S. Pat. No. 5,445,832.

[0022] d) Methods of Solvent Evaporation:

[0023] The drug to be encapsulated, the polymer and the plasticiser aredissolved together in a suitable solvent. This solution is evaporated todryness and the resulting residue reduced down to a suitable size.Examples of this procedure, although not using the plasticiser, can bealso be found in documents such as GB 2,209,937.

[0024] In the present invention, in all cases, the citric acid ester isdeposited along with the polymer, plastifying it and advantageouslymodifying the hydrophobicity, flexibility and coating capacitycharacteristics of the polymer and the release profile of themicro-capsules obtained.

[0025] This is reducing the initial release of the encapsulated drug andmaking this release almost linear in time.

[0026] The present invention is now described by means of following,non-limiting examples:

EXAMPLE 1

[0027] Production of micro-capsules, containing leuprolide acetate,which presents a drug release profile suitable for one month.

[0028] 3 g of tri-ethyl citrate and 1.45 g of lactic-co-glycolic polymer(mw=50000 with monomer ratio of 1/1) are dissolved in 50 ml ofdichloromethane. When the polymer is fully dissolved 67 mg of leuprolideacetate are added and then suspended by sonication.

[0029] 63 g of silicone of 350 cts is added slowly with intensivestirring. And when all the silicone has been added the content of thereactor is poured onto 2.5 l of n-heptane and stirred for 1 hour.

[0030] The micro-capsules are recovered by filtration and dried undervacuum for 48 hours.

EXAMPLE 2

[0031] Production of micro-capsules with one-month release containingoctreotide acetate.

[0032] 2 g of tri-ethyl citrate and 1.45 g of lactic-co-glycolic polymer(mw=50000 with monomer ratio of 1/1) are dissolved in 50 ml ofdichloromethane. When the polymer is fully dissolved 67 mg of octreotideacetate are added and then suspended by sonication.

[0033] 70 g of silicone of 350 cts is added slowly with intensivestirring. And when all the silicone has been added the content of thereactor is poured onto 2.5 l of n-heptane and stirred for 1 hour.

[0034] The micro-capsules are recovered by filtration and dried undervacuum for 48 hours.

EXAMPLE 3

[0035] Production of micro-capsules with a three-month release profilecontaining triptoreline acetate.

[0036] 2 g of tri-ethyl citrate and 1.45 g of lactic-co-glycolic polymer(mw=50000 with monomer ratio of 1/1) are dissolved in 50 ml ofdichloromethane. When the polymer is fully dissolved 45 mg oftriptoreline acetate are added and then suspended by sonication.

[0037] 70 g of silicone of 350 cts is added slowly with intensivestirring. And when all the silicone has been added the content of thereactor is poured onto 2.5 l of heptane and stirred for 1 hour.

[0038] The micro-capsules are recovered by filtration and dried undervacuum for 48 hours.

EXAMPLE 4

[0039] In vitro determination of the drug release by the micro-capsulesobtained.

[0040] Material Needed:

[0041] 12 plastic 10-ml tubes with lid.

[0042] 1 rack for tubes.

[0043] Procedure:

[0044] Approximately 10 mg of micro-capsules containing leuprolideobtained according to example 1 are weighed into 12 10-ml tubes.

[0045] To each tube 2 ml of phosphate buffer 1/30 M and pH=7.0 areadded.

[0046] Each tube is gently shaken to suspend the micro-capsules in thebuffer, the tubes are sealed and placed in an oven at 37° C.

[0047] Taking samples for the control of the hydrolysis is carried outin accordance with the following table: TABLE 1 Taking samples foranalysis of leuprolide released. Tube no. Type of analysis Time 1 h 1, 2Supernatant 3 h 3 Supernatant 6 h 4 Supernatant 1 d 5 and 6  Pellet 2 d7 Pellet 4 d 8 Pellet Point 8 d 10  Pellet 11 d 1 and 11 Pellet 14 d 2Pellet 18 d 3 and 12 Pellet 23 d 9 Pellet 29 d 4 and 5  Pellet

[0048] The analysis of leuprolide released is carried out by HPLC in thefollowing conditions:

[0049] COLUMN: Kromasil C-8; 25×0.45 cm

[0050] ELUENT: Acetonitrile/water 30/70+0.05% trifluoracetic acid

[0051] FLOW RATE: 1 ml/min

[0052] DETECTION: UV 280 nm.

[0053] The samples are taken at the times indicated in table 1 and theanalysis carried out by quantifying the peptide released in thesupernatant (supernatant analysis) or the residual peptide inside themicro-capsule (pellet analysis) depending on the hydrolysis time, asindicated in table 1.

[0054] The result of this analysis is indicated in FIG. 1. In thisfigure, the results obtained are compared with a control assay performedwith leuprolide microcapsules in which diethyl citrate has not beenincorporated, in accordance with the method of example 1.

1. A pharmaceutical preparation of microcapsules of lactic-co-glycoliccopolymer which incorporates a peptide of pharmaceutical interest,characterised in that the copolymer that forms the microcapsulesincorporates a citric acid ester as an additive.
 2. A pharmaceuticalpreparation of microcapsules according to claim 1 characterised in thatthe citric acid ester is selected from triethyl citrate, tributylcitrate and acetyl tributyl citrate.
 3. A pharmaceutical preparation ofmicrocapsules according to claim 2 characterised in that the citric acidester is triethyl citrate.
 4. A preparation according to claim 3characterised in that the amount of triethyl citrate contained in thepreparation varies between 0.1% and 60% by weight of the copolymer.
 5. Apharmaceutical preparation according to claims 1 to 4 characterised inthat the percentage ratio between the lactate and glycolate units in thelactic-co-glycolic copolymer varies between 100% and lactate and 90% ofglycolate, both inclusive.
 6. A pharmaceutical preparation according toany of the previous claims characterised in that the encapsulatedpeptide of pharmaceutical interest is an analogue of LHRH.
 7. Apharmaceutical preparation according to claim 6 characterised in thatthe analogue of LHRH is selected from tryptoreline, leuprolide,gosereline, busereline or cetrorelix.
 8. A pharmaceutical preparationaccording to claims 1 to 5 characterised in that the encapsulatedpeptide of pharmaceutical interest is somatostatine or an analoguethereof.
 9. A pharmaceutical preparation according to claim 8characterised in that the analogue of somatostatine is octreotide.
 10. Apharmaceutical preparation according to claims 1 to 5 characterised inthat the encapsulated peptide of pharmaceutical interest is an analogueof human calcitonine.
 11. A pharmaceutical preparation according toclaim 10 characterised in that the analogue of human calcitonine issalmon calcitonine or carbocalcitonine.